Phosphatidylinositol (hereinafter abbreviated as “PI”) is one of phospholipids in cell membranes. In recent years it has become clear that PI plays an important role also in intracellular signal transduction. It is well recognized in the art that especially PI (4,5) bisphosphate (PI(4,5)P2) is degraded into diacylglycerol and inositol (1,4,5) triphosphate by phospholipase C to induce activation of protein kinase C and intracellular calcium mobilization, respectively [M. J. Berridge et al., Nature, 312, 315 (1984); Y Nishizuka, Science, 225, 1365 (1984)].
Turning back to the late 1980s, PI3K was found to be an enzyme to phosphorylate the 3-position of the inositol ring of phosphatidylinositol [D. Whitman et al., Nature, 332, 664 (1988)].
PI3K was originally considered to be a single enzyme at the time when PI3K was discovered. Recently it was clarified that a plurality of subtypes are present in the PI3K. Three major classes of PI3Ks have now been identified on the basis of their in vitro substrate specificity [B. Vanhaesebroeck, Trend in Biol. Sci., 22, 267(1997)].
Substrates for class I PI3Ks are PI, PI(4)P and PI(4,5)P2. In these substrates, PI(4,5)P2 is the most advantageous substrate in cells. Class I PI3Ks are further divided into two groups, class Ia and class Ib, in terms of their activation mechanism. Class Ia PI3Ks, which include PI3K p110α, p110β and p110δ subtypes, are activated in the tyrosine kinase system. Class Ib PI3K is a110γ subtype activated by a G protein-coupled receptor.
PI and PI(4)P are known as substrates for class II PI3Ks but PI(4,5)P2 is not a substrate for the enzymes of this class. Class II PI3Ks include PI3K C2α, C2β and C2γ subtypes, which are characterized by containing C2 domains at the C terminus, implying that their activity will be regulated by calcium ions. The substrate for class III PI3Ks is PI only. A mechanism for activation of the class III PI3Ks is not clarified yet. Since each subtype has its own mechanism for the regulating activity, it is considered that the respective subtypes will be activated depending on their respective stimuli specific to each of them.
In the PI3K subtypes, the class Ia subtype has been most extensively investigated to date. The three subtypes of class Ia are hetero dimers of a catalytic 110 kDa subunit and regulatory subunits of 85 kDa and 55 kDa. The regulatory subunits contain SH2 domains and bind to tyrosine residues phosphorylated by growth factor receptors with a tyrosine kinase activity or oncogene products thereby inducing the PI3K activity of the p110 catalytic subunit. Thus, the class la subtypes are considered to be associated with cell proliferation and carcinogenesis. Furthermore, the class Ia PI3K subtypes bind to activated ras oncogene to express their enzyme activity. It has been confirmed that the activated ras oncogene is found to be present in many cancers, suggesting a role of class Ia PI3Ks in carcinogenesis.
As explained above, PI3K inhibitors are expected to be a novel type of medicaments useful against cell proliferation disorders, especially as carcinostatic agents. As for the PI3K inhibitor, wortmannin [H. Yano et al., J. Biol. Chem., 263, 16178 (1993)] and LY294002 [J. Vlahos et al., J. Biol. Chem., 269, 5241(1994)] which is represented by the formula below are known. However, development of PI3K inhibitors having a more potent cancer cell growth inhibiting activity is desired. 
Japanese Patent KOKAI (Laid-Open) No. 6-220059 discloses fused heteroaryl derivatives shown by formula (a) below which possess an activity of reducing the blood glucose level. Furthermore, compounds shown by formula (b) and formula (c) below are described in Indian J. Chem., Sect. B (1993), 32B (9), 965-8 and J. Heterocycl. Chem. (1992), 29 (7), 1693-702, respectively. In addition, Al-AzharBull. Sci. (1992), 3(2), 767-75 discloses a compound shown by formula (d) below. However, none of these prior art publications disclose or suggest the PI3K inhibiting activity. 
In formula (a) above, Z is O, S or ═N—R0, R1 is an amino which may be substituted, a heterocyclic group which may be substituted, etc.; R2 is cyano, an amino which may be substituted, or a heterocyclic group which may be substituted; and with respect to the remaining substituents, see the specification of the patent. In formula (b) and (c) above, R is a (substituted) amino or a (substituted) nitrogen-containing saturated heterocyclic group.
Publication No. WO98/23613 discloses fused pyrimidine derivatives, such as 7H-pyrrolo[2,3-d]pyrimidine derivatives, which having a tyrosine kinase receptor inhibiting activity and which are useful as carcinostatic agents, wherein the fused pyrimidine derivatives have at its fourth position a particular-heteroaryl-substituted amino, pheny-substituted amino, or indole-1-yl, and have no substituent at its second position.
Following compounds are known among the compounds shown by general formula (I), whereas “A” ring is a ring shown by (b);
(1) Ann. Pharm. Fr. (1974), 32(11), 575-9 discloses 4-(4-morpholinyl)-2-phenylpirido[2,3-d]pyrimidine as a compound having antiinflammatory and spasmolytic activities,
(2) Chem. Pharm. Bull. (1976), 24(9), 2057-77 discloses 4-(4-morpholinyl)-2-phenylpirido[2,3-d]pyrimidine-7(1H)-one as a compound having a diuretic activity,
(3) Khim.-Farm. Zh. (1993), 7(7), 16-19 and Khim. Geterotsiki. Soedin. (1971), 7(3), 418-20 disclose 4-(4-morpholinyl)-2-phenyl-6-quinazolinol and 6-methoxy-4-(4-morpholinyl)-2-phenylquinazoline as compounds having an antibiotic activity,
(4) Publication No. WO2000/41697 discloses 2,4-diamino-6-phenyl-8-piperidinopyrimido[5,4-d]pyrimidine as a compound having cerebral ischemia prevention and treatment effects,
(5) Publication No. WO99/32460 discloses, as cardiovascular drugs, compounds of general formula (Ib) described hereinafter wherein B is a benzene ring, W is N, n is 2 or 3, existing R1's are all —OMe, and R4b is an unsubstituted phenyl or a phenyl substituted by 1 to 3 substituents which are selected from -a halogen, NO2, -a lower alkyl, —O-a lower alkyl, -a halogenated lower alkyl and —CONRaRc,
(6) Publication No. BE841669 discloses, as antiparasitics, compounds of general formula (Ib) described hereinafter wherein B is a benzene ring, W is N, n is 1, R1 is -a halogen or -a lower alkyl, and R4b is -(an imidazolyl which may have one or more substituents),
(7) Publication No. WO99/43682 discloses, as antianxiety agents, compounds of general formula (Ib) described hereinafter wherein B is a thiophene ring, and W is CII,
(8) Japanese Patents KOKAI (Laid-Open) Nos. 62-10085 and 61-158983 disclose compounds of general formula (Ib) described hereinafter wherein B is an imidazole ring, and W is N, whereas the compounds have an antiinflammatory activity, a platelet aggregation inhibiting activity, etc.,
(9) U.S. Pat. No. 3,873,545 and Act Pol. Pharm. (1994), 51(4-5), 359-63 disclose compounds of general formula (Ib) described hereinafter wherein B is a pyridine ring, and R4b is an unsubstituted phenyl, an unsubstituted pyridyl, or -a lower alkylene-(a nitrogen-containing saturated heterocyclic group which may have one or more substituents), whereas the compounds have a spasmolytic, diuretic or hypotensive activity,
(10) U.S. Pat. No. 2,940,972 discloses compounds of general formula (Ib) described hereinafter wherein B is a pyrazine ring, and R4b is an unsubstituted phenyl, or a benzyl, whereas the compounds have a coronary dilating or sedative activity,
(11) U.S. Pat. No. 3,753,981 and German Patent Publication No. 2,140,280 disclose compounds of general formula (Ib) described hereinafter wherein B is a benzene ring, and R4b is a styryl or 2-(5-nitro-2-furyl)vinyl, whereas the compounds have an antiinflammatory or antibiotic activity, and
(12) Eur. J. Med. Chem. (1996), 31(5), 417-425, discloses compounds of general formula (Ib) described hereinafter wherein B is a benzene ring, W is CH, and R2 and R3 are bonded together with an adjacent N atom to form -(piperidinyl which may have one or more substituents) or -(piperazinyl which may have one or more substituents), as compounds working as a benzodiazepine receptor ligand, U.S. Pat. No. 4,560,692 discloses them as those having a spasmolytic and ataractic activity, and Japanese Patents KOKAI (Laid-Open) No. 2-129169 discloses them as those having a lipoperoxidation inhibiting activity.
Furthermore, compounds of general formula (Ib) described hereinafter wherein B is a pyridine ring and n is 0 are disclosed in Japanese Patent KOKAI (Laid-Open) No. 51-138689 (antiparasitics), Japanese Patent KOKAI (Laid-Open) No. 56-120768 (a dye component for thermosensitive recording materials), Antimicrob. Agents Chemother., (1975), 8 (2), 216-19 (an antibacterial activity), Cancer Res. (1975), 35 (12), 3611-17 (a mutagenic activity), CA 64: 19608c, Collect. Czech. Chem. Commun., (1994), 59 (6), 1463-6, U.S. Pat. No. 5,304,554 (an anti-HIV activity), Chem. Pharm. Bull., (1982), 30(6), 1974-9, and J. Heterocycl. Chem. (1980), 17(5), 1029-34. However, none of the prior publications teach or even suggest the PI3K inhibiting activity and carcinostatic activity.